From cc6003916ed46d7a67d91ee32de0f9138047d55f Mon Sep 17 00:00:00 2001 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> Date: Sat, 21 Jan 2023 12:39:42 +0900 Subject: lib/Kconfig.debug: do not enable DEBUG_PREEMPT by default In workloads where this_cpu operations are frequently performed, enabling DEBUG_PREEMPT may result in significant increase in runtime overhead due to frequent invocation of __this_cpu_preempt_check() function. This can be demonstrated through benchmarks such as hackbench where this configuration results in a 10% reduction in performance, primarily due to the added overhead within memcg charging path. Therefore, do not to enable DEBUG_PREEMPT by default and make users aware of its potential impact on performance in some workloads. hackbench-process-sockets debug_preempt no_debug_preempt Amean 1 0.4743 ( 0.00%) 0.4295 * 9.45%* Amean 4 1.4191 ( 0.00%) 1.2650 * 10.86%* Amean 7 2.2677 ( 0.00%) 2.0094 * 11.39%* Amean 12 3.6821 ( 0.00%) 3.2115 * 12.78%* Amean 21 6.6752 ( 0.00%) 5.7956 * 13.18%* Amean 30 9.6646 ( 0.00%) 8.5197 * 11.85%* Amean 48 15.3363 ( 0.00%) 13.5559 * 11.61%* Amean 79 24.8603 ( 0.00%) 22.0597 * 11.27%* Amean 96 30.1240 ( 0.00%) 26.8073 * 11.01%* Link: https://lkml.kernel.org/r/20230121033942.350387-1-42.hyeyoo@gmail.com Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Acked-by: Roman Gushchin Acked-by: Mel Gorman Acked-by: Davidlohr Bueso Cc: Ben Segall Cc: Christoph Lameter Cc: Daniel Bristot de Oliveira Cc: David Rientjes Cc: Dennis Zhou Cc: Dietmar Eggemann Cc: Ingo Molnar Cc: Johannes Weiner Cc: Joonsoo Kim Cc: Juri Lelli Cc: Matthew Wilcox Cc: Muchun Song Cc: Pekka Enberg Cc: Peter Zijlstra Cc: Shakeel Butt Cc: Steven Rostedt (Google) Cc: Tejun Heo Cc: Valentin Schneider Cc: Vincent Guittot Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- lib/Kconfig.debug | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'lib/Kconfig.debug') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 918bda4ee120..a97aca81db24 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1246,13 +1246,16 @@ config DEBUG_TIMEKEEPING config DEBUG_PREEMPT bool "Debug preemptible kernel" depends on DEBUG_KERNEL && PREEMPTION && TRACE_IRQFLAGS_SUPPORT - default y help If you say Y here then the kernel will use a debug variant of the commonly used smp_processor_id() function and will print warnings if kernel code uses it in a preemption-unsafe way. Also, the kernel will detect preemption count underflows. + This option has potential to introduce high runtime overhead, + depending on workload as it triggers debugging routines for each + this_cpu operation. It should only be used for debugging purposes. + menu "Lock Debugging (spinlocks, mutexes, etc...)" config LOCK_DEBUGGING_SUPPORT -- cgit v1.2.3